Many machines throughout industry have joints which can rotate around a pivot point. An example of a joint rotating around a pivot point is a ball and socket joint. Another example of such a joint would be a joint having two gimbals so constructed that the rotational axes of the gimbals are mutually perpendicular to one another. For a number of reasons, it is often undesirable for these joints to rotate beyond an acceptable range of motion.
Joint rotation is usually dictated by the movement of rods or other apparatus connected to the joint. In many cases, the movement of rods or other apparatus connected to a joint is driven mechanically. There are several kinds of mechanical driving systems, including hydraulic cylinder systems or screw systems.
An electrical controller can be used to coordinate the movement of rods and the rotation of joints. A controller is usually programmed to maintain the rotation of joints within an acceptable range of motion. Sometimes, however, joints may get rotated beyond limits. This may happen because of bugs in software, or other design or setup flaws.
It is therefore desirable to have a system that can detect when a joint is on the verge of being rotated too far. U.S. Pat. No. 2,828,458 shows a limit switch system designed to do this, but this limit switch is complex and has many mechanical components. Such a limit switch system is not practical for complicated machines having many joints. It is too bulky, and each of the numerous components of the switch provide an opportunity for the switch to fail.
Electrically controlled machines can get very complicated and have many joints. One such machine is disclosed in U.S. Pat. No. 4,988,244. That machine, as well as others, can crash if one or more joints are rotated beyond a limit of acceptable motion. It can therefore be appreciated that a mechanically simple, reliable, and durable means for detecting a limit of acceptable joint rotation is desirable.